iOS UserDefaults Intermittently Returns Nil After getPreferences() Call - Race Condition?

iOS Intermittent Bug: UserDefaults Preferences Loading Issue

Problem Summary

We're experiencing an intermittent issue where UserPreferences.shared.preferences returns inconsistent values even after calling getPreferences(). The behavior is unpredictable and affects critical functionality.

Environment

• iOS Version: 15+
• Language: Objective-C with Swift interop
• Storage: UserDefaults with App Group (group.com.jci.tyco.glss)
• Architecture: Singleton pattern for UserPreferences (Swift class)

The Issue

When a push notification arrives and triggers the showEvent: method, user preferences are sometimes loaded correctly and sometimes return nil or default values:

Scenario A (Works - ~60% of time):

Scenario B (Fails - ~40% of time):

Observed Pattern

From extensive logging over multiple test runs:

Key Observation:

• At app launch: Preferences often load successfully
• Seconds later when push arrives: Same preferences become unavailable
• User navigates to another screen and back: Preferences suddenly work again

Code Structure

Objective-C AppDelegate.m

- (void)showEvent:(FMEvent *)event eventReadSource:(FMEventReadSourceType)eventSource {
    BOOL isUserRoleEndUser = [[FMUserRolesRepository instance] userRoleAvailable:FMUserRoleEndUser];
    
    UserPreferences *userPrefs = [UserPreferences shared];
    [userPrefs getPreferences];  // ← Called here
    
    // Immediately after, sometimes nil!
    bool hasFireAudio = [userPrefs.preferences.fireAudio.lowercaseString isEqual:@"true"];
    
    NSLog(@"isUserRoleEndUser: %d | Fire Audio: %d", isUserRoleEndUser, hasFireAudio);
    
    // Decision logic based on preferences
    if ([FMConstants getUserRegion] == UserRegionUK && 
        isUserRoleEndUser &&
        userPrefs.preferences &&  // ← Sometimes nil here
        hasFireAudio) {
        // Show Screen A
    } else {
        // Show Screen B
    }
}

```class UserPreferences: NSObject {
    static let shared = UserPreferences()
    
    var preferences: FMUserPreferencesInfo?  // ← This becomes nil intermittently
    
    func getPreferences() {
        let userDefaults = UserDefaults(suiteName: "group.com.jci.tyco.glss")
        
        if let data = userDefaults?.data(forKey: "UserPreferences") {
            // Decode and set preferences
            self.preferences = // decoded object
        } else {
            // Create default preferences with fireAudio = "false"
            self.preferences = FMUserPreferencesInfo()
        }
    }
}